Recent highly-integrated semiconductor devices require a severer quality of a silicon wafer used as a substrate for such semiconductor devices. In particular, there is a strong demand for the development of a silicon wafer having less grown-in defects in the device active region.
A technique of performing heat treatment on a silicon wafer at high temperature is well known as a process for reducing such grow-in defects.
As one example of such a technique, there is a technique of heat treating a silicon wafer at a temperature range of 1000° C. or higher and 1350° C. or lower for 50 hours or less in a hydrogen and/or inert gas atmosphere, followed by oxidation heat treatment at a temperature range of 800° C. or higher and 1350° C. or lower for 50 hours or less (for example, Patent Document 1).
There is also known a technique of heat treating a silicon single crystal wafer at a temperature of from 1100 to 1300° C. in a non-oxidizing atmosphere for 1 minute or more and heat treating the resulting wafer continuously at a temperature of from 700 to 1300° C. in an oxidizing atmosphere for 1 minute or more without cooling it to a temperature less than 700° C., thereby forming a silicon oxide film on the surface of the wafer (for example, Patent Document 2).
In recent years, a technique for subjecting a silicon wafer to rapid heating/cooling thermal process (RTP: Rapid Thermal Process) is known as a technique of producing, in a high productivity and an easy manner, a silicon wafer with few defects in the surface layer of the wafer.
As one example, there is known a technique of heating a material for substrate obtained from a silicon single crystal having an oxygen concentration of from 11 to 17×1017 atoms/cm3 (ASTMF121-79) at from 1100 to 1280° C. for from 0 to 600 seconds in an atmosphere containing nitrogen in an amount of 90% or more and then cooling it at a cooling rate of from 100 to 25° C./sec in an atmosphere switched to that containing oxygen in an amount of 10% or more (for example, Patent Document 3).
As another example, there is known a technique in which the temperature in the RTP apparatus is suddenly increased at the predetermined first temperature heating rate to the first temperature (for example, 1120° C.-1180° C.), it is continued at the first temperature for a certain time period. Next, it suddenly decreases at the predetermined first temperature cooling rate to the second temperature (for example, 800° C.), it is continued at the second temperature for a certain time period. Afterwards, it suddenly increases at the predetermined second temperature heating rate to the third temperature (for example, 1200° C.-1230° C.) that is higher than the first temperature, it is continued at the third temperature for a certain time period (for example, Patent Document 4).